Controlling the stiffness of a hollow metal bat by providing helical internal ribs

ABSTRACT

A hollow metal bat comprising an elongated tubular structure having a barrel portion, a handle portion and a tapered portion connecting the barrel portion to the handle portion, and further comprising at least one helical internal rib formed along at least a portion of the elongated tubular structure.

REFERENCE TO PENDING PRIOR PATENT APPLICATION

This patent application claims benefit of pending prior U.S. ProvisionalPatent Application Ser. No. 61/448,063, filed Mar. 1, 2011 by MatthewFonte for CONTROLLING THE STIFFNESS OF A METAL BAT BY CREATING INTERNALRIBS (Attorney's Docket No. FONTE-5 PROV), which patent application ishereby incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates to baseball bats and softball bats in general,and more particularly to metal baseball bats and metal softball bats.

BACKGROUND OF THE INVENTION

Baseball bats and softball bats (hereinafter sometimes referred tosimply as “bats”) are well known in the art. Originally, bats were madeof wood. However, more recently, some bats (and particularly softballbats) have been made of metal. In general, metal bats are made with ahollow construction in order to reduce their weight. See FIG. 1, whichshows an exemplary hollow metal bat.

Metal bats exhibit two types of vibrational modes, i.e., bending modesand hoop modes. Bending modes relate to vibrations which extend alongthe longitudinal axis of the bat. See FIG. 2, which shows exemplarybending modes for a hollow metal bat. Hoop modes are unique to hollowbats and involve only a radial vibration of the barrel of the bat. SeeFIG. 3, which shows exemplary hoop modes for a hollow metal bat. Thelowest-frequency hoop mode is responsible for both the “ping” sound of ahollow metal bat and the so-called “trampoline effect” (i.e., the springeffect of the barrel of the bat when it encounters the ball).

Modal analysis is used to determine the mode shapes and frequencies fora wide variety of bats. In general, higher bat performance (with respectto batted ball speed) tends to be achieved with bats which have lowerhoop frequencies.

Thus, a primary objective of the present invention is to provide a newhollow metal bat which is characterized by lower hoop frequencies andhence improved bat performance.

SUMMARY OF THE INVENTION

In accordance with the present invention, one or more helical internalribs are formed on the interior of the hollow metal bat in order tocontrol the stiffness of the bat and thereby lower hoop frequencies (andhence improve bat performance). The helical internal ribs also help tominimize bending failure modes and hoop failure modes. The one or morehelical internal ribs may vary in frequency (i.e., number), pitch,height and width profile in order to provide the bat with the desiredperformance characteristics. Among other things, the goal of theinvention is to coordinate the frequency (i.e., number) of the spiralribs disposed about the inner circumference of the bat barrel, and thepitch, height and width profile of those ribs, so as to allow thecreation of a thin wall, light weight bat barrel, while tuning (i.e.,controlling) the stiffness of the barrel. Controlling the stiffness ofthe barrel consequently controls the “trampoline effect” of the barrel,whereby to ensure maximum bat performance while staying within batregulations. Without helical internal ribs, the only other way tocontrol the stiffness of the bat is to either (i) increase the thicknessof the side wall of the bat (which is undesirable since it increases theweight of the bat), and/or (ii) form the bat out of a material which hasa higher modulus of elasticity (which typically means using a denser,and hence heavier, material).

U.S. Pat. No. 5,931,405 discloses a metal bat having internal grooveswhich are circumferential in nature, and which are machined into theinterior side wall of the bat. However, these grooves are cavities,i.e., recesses formed in the side wall of the bat, and their purpose issimply to reduce the weight of the metal bat. Thus, the grooves of U.S.Pat. No. 5,931,405 are the structural inverse of the positive ribs ofthe present invention (i.e., they are recesses rather than theprojections of the present invention). Furthermore, the internal groovesof U.S. Pat. No. 5,931,405 have a different configuration than the ribsof the present invention (i.e., they are circumferential rather thanhelical). And, significantly, the purpose of the surface grooves of U.S.Pat. No. 5,931,405 is different than the purpose of the helical internalribs of the present invention (i.e., the surface grooves are forweight-reduction rather than strength increase). Also, the method ofmaking the internal grooves of U.S. Pat. No. 5,931,405 is different fromthe method of making the helical internal ribs of the presentinvention—specifically, the grooves of U.S. Pat. No. 5,931,405 are madeby machining away wall thickness, whereas the spiral ribs of the presentinvention are formed on the interior wall of the bat during cold working(i.e., flowform, swaging, impact extruding, drawing, etc.). The coldwork process used to form the helical internal ribs of the presentinvention provides a microstructure which is metallurgically-superior tothe microstructure provided by the “machined-away” process used to formthe internal grooves of U.S. Pat. No. 5,931,405. And, furthermore, thecircumferential ribs of U.S. Pat. No. 5,931,405 have little effect onthe bending modes of the bat.

U.S. Pat. No. 2,340,156 relates to “cast integral” longitudinal ribs.These longitudinal ribs have little effect on the hoop modes of the bat.In contrast, the helical internal ribs of the present invention improveboth the hoop modes and the bending modes of the hollow metal bat.Furthermore, the “cast integral” casting of U.S. Pat. No. 2,340,156 isdone hot, yielding cast grains which are large, often brittle andsusceptible to fracture—all features which are undesirable in a bat. Incontrast, the cold worked helical internal ribs of the present inventionprovide both dimensionally—and metallurgically—superior ribs.

In one preferred form of the invention, there is provided a hollow metalbat comprising an elongated tubular structure having a barrel portion, ahandle portion and a tapered portion connecting the barrel portion tothe handle portion, and further comprising at least one helical internalrib formed along at least a portion of the elongated tubular structure.

In another preferred form of the invention, there is provided a methodfor forming a hollow metal bat, the method comprising:

positioning a preform on a mandrel, wherein the mandrel comprises atleast one helical groove; and

applying compression to the outside diameter of the preform so as toform an elongated tubular structure having a barrel portion, a handleportion and a tapered portion connecting the barrel portion to thehandle portion, and further comprising at least one helical internal ribformed along at least a portion of the elongated tubular structure.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and features of the present invention will bemore fully disclosed or rendered obvious by the following detaileddescription of the preferred embodiments of the invention, which is tobe considered together with the accompanying drawings wherein likenumbers refer to like parts, and further wherein:

FIG. 1 is a schematic view of an exemplary prior art hollow metal bat;

FIG. 2 is a schematic view showing exemplary bending modes of a hollowmetal bat;

FIG. 3 is a schematic view showing exemplary hoop modes of a hollowmetal bat;

FIG. 4 is a schematic view, partially broken away, showing a new andimproved hollow metal bat formed in accordance with the presentinvention;

FIG. 5 is a side sectional view of the hollow metal bat shown in FIG. 4;

FIG. 5A is a schematic view showing a section of the barrel portion of ahollow metal bat having a plurality of helical internal ribs;

FIG. 6 is a schematic view showing that hollow metal bats with lowerhoop frequency have increased performance;

FIG. 7 is a schematic view of a bat;

FIG. 8 is a schematic view showing the optimal hoop frequency of analuminum bat;

FIG. 9 is a schematic view showing exemplary bending modes of a hollowmetal bat;

FIG. 10 is a schematic view showing exemplary hoop modes of a hollowmetal bat;

FIG. 11 is a schematic view showing a preferred rib design;

FIG. 12 is a schematic view showing exemplary buckling deformations of atube;

FIG. 13 is a schematic view comparing the balance point of various bats;

FIG. 13A is a schematic sectional view showing a multi-wall bat formedin accordance with the present invention;

FIG. 14 is a schematic view showing a flowforming process;

FIG. 15 is a schematic view showing longitudinal ribs formed inside ahollow metal bat; and

FIG. 16 is a schematic view showing helical ribs formed inside a hollowmetal bat.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides a new and improved hollow metal bat whichadvantageously addresses various aspects of bat design, as discussedherein.

Looking first at FIGS. 4 and 5, there is shown a new and improved hollowmetal bat 5 which generally comprises an elongated tubular structure 10having a barrel portion 15, a handle portion 20 and a tapered portion 25connecting barrel portion 15 to handle portion 20. An end cap 30 closesoff the distal end of barrel portion 15, and a knob 35 closes off theproximal end of handle portion 20.

In accordance with the present invention, one or more helical internalribs 40 is formed along at least a portion of elongated tubularstructure 10. More particularly, one or more helical internal ribs 40 isformed along at least a portion of barrel portion 15 and, in onepreferred form of the invention, the one or more helical internal ribs40 is formed along substantially the entire barrel portion 15. In oneparticularly preferred form of the present invention, one or morehelical internal ribs 40 extends along substantially the entire lengthof bat 5. Preferably a plurality of helical internal ribs 40 are formedon hollow metal bat 5. See, for example, FIG. 5A, which shows a sectionof the barrel portion 15 of a hollow metal bat 5 having a plurality ofhelical internal ribs 40. The one or more helical internal ribs 40 mayvary in frequency (i.e., number), pitch, height and width profile inorder to provide the bat with the desired performance characteristics.

Furthermore, if desired, the pitch, height and/or width profile of eachhelical internal rib 40 may vary along the length of the rib.

By providing bat 5 with one or more helical internal ribs 40, and byvarying the frequency (i.e., number), pitch, height and width profile ofthose ribs, various aspects of bat design can be advantageouslyaddressed, as will hereinafter be discussed.

Regulatory Constraints

Regulatory constraints on bat designs, and specifically non-wood batdesigns, are making it increasingly difficult to engineer superiorperformance while remaining within regulatory standards.

One standard for testing baseball bat performance is the NationalCollegiate Athletic Association (NCAA) Bat-Ball Coefficient ofRestitution (BBCOR) protocol which became effective on Jan. 1, 2011.This protocol has been adopted as an addendum to the NCAA standard ASTMF2219, Standard Test Methods for Measuring High-Speed Bat Performance.For a bat to adhere to the new BBCOR standard, it must meet thefollowing criteria:

-   -   size and weight specifications;    -   length-weight ratio;    -   Moment of Inertia (MOI) requirement (based the bat's length        class);    -   the bat ring must pass over the entire length of the bat before        and after every hit; and    -   the BBCOR must not exceed 0.500.

The Bat-Ball Coefficient-of-Restitution (BBCOR) measures the combinedelastic properties of the bat-ball system as a function of hoopfrequency. The solid curve shown in FIG. 6 is a theoretical predictionfrom a simple mass-spring model of the “trampoline effect” of thebat-ball system, and the data points represent the measured BBCOR values(extracted from the original field study data by Alan Nathan) for thefive metal bats used in the Grisco-Greenwald batting cage study. Theplot in FIG. 6 shows that the higher performing bats have a lower hoopfrequency, which indicates that the simple mass-spring model of thetrampoline effect captures the essential physics of the bat-ball system.

There is a fine line between optimizing bat performance and notexceeding the new BBCOR standard. Significantly, the present inventionprovides one method for doing so, i.e., by providing a hollow metal batthat uses helical internal ribs in its wall thickness to improve orcontrol bat stiffness. In this respect it should be appreciated thatlongitudinal ribs increase the bending stiffness of a bat, whilecircumferential ring ribs control its hoop stiffness. The new helicalinternal ribs of the present invention simultaneously control bothstiffnesses (i.e., bending stiffness and hoop stiffness) of the bat. Thetapered handle of the bat can also have internal helical ribs which cancontrol stiffness in the non-barrel section of the bat. Without helicalinternal ribs, the thickness of the side wall of the bat would have tobe increased in order to increase the bending and hoop stiffnesses,which would add undesirable weight to the bat. Adding helical internalribs to the bat increases the Moment of Inertia, which increases thebending stiffness, i.e.,

Bending stiffness=E×I

where E=Young's Modulus and I=Moment of Inertia.

Preferably, the height of the helical internal ribs should be less thanthe wall thickness of the bat in order to keep sinking to a minimum. Inone preferred form of the invention, the height of the ribs ranges fromabout 40% to about 60% of the thickness of the side wall of the bat. Inaddition, the helical internal ribs are preferably attached to the base(i.e., to the side wall of the bat) with generous radii at the cornerswhere the helical internal ribs meet the side wall of the bat. Thehelical internal ribs of the present invention can be spiraled to thecenter line of the bat, and/or can vary in frequency (i.e., number)around the circumference of the inner barrel and/or inner taperedsection of the bat, and/or can vary in pitch, height and width profilealong the length of the bat. The helical internal ribs of the presentinvention can be engineered so as to (i) allow the bat to have a thinnerbarrel wall thickness, thereby making the bat lighter (and hence able tobe swung faster), (ii) enhance bat strength for durability so as toprevent denting or plastic deformation during usage, (iii) increase thebarrel's “sweetspot” by tailoring its stiffness along the barrel, and(iv) design/tune the barrel's stiffness so as to maximize its“trampoline effect” for optimal BBCOR performance without violatingregulatory constraints.

Bat Speed

As discussed above, by providing helical internal ribs in hollow metalbats, the bats can be provided with increased durability and improvedperformance characteristics.

As seen in FIG. 7, bats typically include a handle portion, a barrelportion, and a tapered portion joining the handle portion to the barrelportion.

The barrel of these bats is generally formed from aluminum or anothersuitable metal, and/or one or more composite materials. Barrels having asingle-wall construction, and more recently a multi-wall construction,have been developed. Modern metal bats typically include a hollowinterior, such that the bats are relatively lightweight and allow a ballplayer to generate substantial “bat speed” or “swing speed”—the lighterthe bat, the faster it can be swung, and hence the further the ball willgo. In accordance with the present invention, helical internal ribs canbe provided on the interior of single-wall bats and double-wall bats(with double-wall bats, the ribs may be formed on the inner and/or outersleeves) so as to reduce bat weight and hence improve bat speed.

Durability

While it is generally desirable to have a light bat, it is alsoimportant that the bat be durable enough that it will not dent whenhitting the ball. As such, barrel wall thicknesses are often designed tobe heavier than desired so as to prevent denting or plastic deformationof the bat during usage. However, with the present invention, thehelical internal ribs of the bat can be used to strengthen a very thin,light-weight bat wall. Such helical internal ribs can be used onsingle-wall bats and double-wall bats (with double-wall bats, the ribsmay be formed on the inner and/or outer sleeves) so as to improve batstrength and durability while minimizing bat weight. Helical or spiralribs provide reinforcement for the thin wall barrel in both the bending(longitudinal) and hoop (radial) directions.

Sweetspot

The “sweetspot” of a bat is the portion of the barrel which, when struckby the ball, provides maximum batting performance. It is the location onthe barrel at which the collision between ball and bat occurs withmaximum efficiency and with the transmission of minimum vibrationthrough the bat to the hands of a user. While highly subjective, manyplayers would accept the proposition that the sweetspot of the bat has adimension of approximately 2 inches in length, and possibly up to 4inches in length, and is located generally midway along the barrelportion of the bat. It will be appreciated that it is highly desirableto provide an improved bat with the largest possible sweetspot whileremaining within bat regulations. By providing a hollow metal bat withthe helical internal ribs of the present invention, and by varying thefrequency (i.e., number), pitch, height and width profile of those ribs,the axial and radial stiffnesses of the bat can be varied along thebarrel so as to increase the sweetspot of the bat. Additionally, bythickening the barrel wall in the area of the sweetspot, and byproviding the helical internal ribs of the present invention, an optimalsweetspot configuration can be achieved. Furthermore, by providinghelical internal ribs in the tapered handle of the bat, vibration can bedampened, whereby to provide a vibration-free, “soft” feel to the bat.

“Trampoline Effect”

Hollow metal bats typically exhibit a phenomenon known as the“trampoline effect”, which essentially refers to the rebound velocity ofa ball leaving the barrel of the bat as a result of dynamic couplingbetween the bat and the ball. It is desirable to construct a bat havinga high “trampoline effect” so that the bat may provide a high reboundvelocity to a pitched ball upon contact. The “trampoline effect” is adirect result of matching the fundamental frequencies between the batand the ball (dynamic coupling), and the resulting compression andstrain recovery of the bat barrel. During this process of barrelcompression and decompression, energy is transferred to the ballresulting in an effective Coefficient of Restitution (COR) of the ball,which is the ratio of the post impact ball velocity to the incident ballvelocity, i.e.,

COR=Vpost impact/Vincident

In other words, in general, the COR of the ball improves as the“trampoline effect” increases.

There is a need to tailor the trampoline effect of the bat so as tomaximize the ball's COR, while still engineering the bat to be withinbat regulations. In accordance with the present invention, helicalinternal ribs can be provided on single-wall bats and double-wall bats(with double-wall bats, the ribs may be formed on the inner and/or outersleeves) so as to control and/or maximize the “trampoline effect” of thebat, yet remain within bat regulations.

See FIG. 8, which shows the optimal hoop frequency of an aluminumbarrel.

For the new NCAA regulations, the maximum allowable BBCOR is 0.500.Therefore, it is desirable to tailor the hoop frequency (i.e., barrelstiffness) of the bat so that its “trampoline effect” is consistentlyoptimized for a BBCOR of between 0.465-0.500 (and still meet the otherbat regulations). As a point of reference, wood bats typically have a0.462 BBCOR. In accordance with the present invention, the BBCOR of thebat may be specified by providing helical internal ribs of theappropriate frequency (i.e., number), pitch, height and width profile.

Hoop Frequency

During the collision between the ball and the bat, a large amount ofkinetic energy is lost when the ball deforms and compresses around thebarrel of the bat. In a wood bat, the barrel of the bat is essentiallyrigid, such that all of the deformation associated with the bat-ballcollision occurs in the ball. However, in hollow non-wood (e.g., metal)bats, the barrel can flex during the collision. Thus, the ball typicallydeforms less when impacting the relatively “flexible” barrel of a hollowmetal bat than when impacting the relatively inflexible barrel of a woodbat. Significantly, with a hollow metal bat, less energy is dissipatedby the ball due to the reduced ball deformation, and the energy used tocompress the barrel of the bat can be returned to the ball as the barrelrebounds. This phenomenon of barrel flexing is known as the “trampolineeffect”. The rate at which the trampoline effect occurs is related tothe mass and stiffness of the barrel of the bat and, therefore, to oneof the natural frequencies of the barrel of the bat. The naturalfrequency at which the bat trampoline effect occurs is theaforementioned hoop mode. As noted above, the frequency (i.e., number),pitch, height and width profile of the helical internal ribs can bedesigned to stiffen the bat so as to control the hoop frequencies. Inaddition, as also noted above, bending modes are also important toconsider during hitting. Again, the frequency (i.e., number), pitch,height and width profile of the helical internal ribs can be designed tostiffen the bat so as to control the bending frequencies. In thepreferred form of the invention, the frequency (i.e., number), pitch,height and width profile of the helical internal ribs are designed tostiffen the bat so as to control both the bending and hoop frequencies.

See FIGS. 9 and 10, which show exemplary bending modes and hoop modes,respectively, of a hollow metal bat.

Internal Ribs in the Barrel and Tapered Section

As noted above, a primary reason for adding helical internal ribs in ahollow metal bat design is to improve the stiffness of the barrel andtapered sections of the bat. Helical internal ribs do this by increasingstiffness in the different sections of the bat where required. Becausestiffness is a function of Young's Modulus and the Moment of Inertia,stiffness can also be improved by increasing the modulus of thematerial. However, moving from a material having a lower modulus (e.g.,an aluminum alloy) to a material having a higher modulus, stiffermaterial (e.g., steel, stainless steel and/or a Titanium alloy) addsundesirable weight to the bat. Significantly, by utilizing the spiraledstiffening ribs of the present invention, it is now possible to use amaterial heavier than aluminum without increasing the overall weight ofthe bat, because the helical internal ribs can be used to add strengthand stiffness to a very thin bat, e.g., a non-aluminum bat.

The frequency (i.e., number), pitch, height and width profile of thehelical internal ribs can be varied so as to adjust bat stiffness. SeeFIG. 11, which shows one preferred rib profile.

The height of the helical internal rib is preferably less than thethickness of the adjoining wall, with the relative dimensions dependingon loads, the frequency (i.e., number) of the helical internal ribsaround the circumference of the bat, the pitch of the helical internalribs, the width profile of the helical internal ribs, etc. at barrelscan buckle, collapse, dent and even break from the buckling loads duringbarrel-ball contact, and the helical internal ribs of the presentinvention can help support the loads without adding significant weightto the bat.

See FIG. 12, which provides a schematic illustration of exemplarybuckling of a barrel of a bat.

Center of Mass

The center of mass (CM) is also known as the balance point. The closerthe CM is to the handle of the bat, the easier it is to swing the bat.FIG. 13 compares the balance points of four 30″ youth bats: three woodbats of weights 26 oz, 23 oz, and 20 oz, and one aluminum bat of weight27 oz. The balance point for all three of the wood bats is located atthe same place, which is to be expected since the profile shapes of thethree bats are the same and they are all made from solid wood, so thebalance point should be the same for all three bats regardless of theirrespective weights. In contrast, the balance point of the aluminum batis more than an inch closer to the handle than the balance point for thewood bats—as a result, even though the aluminum bat is heavier than thewood bats, it is actually easier to swing since its balance point iscloser to the handle. Thus, the swing weight of a bat is a function ofboth bat weight and the center of mass, which is the reason that not all28 oz softball bats swing the same. An end-loaded bat can have the sameweight as a normal bat, but will feel heavier because more of the massis distributed towards the barrel end of the bat.

Technically, this all relates to the Moment of Inertia of the bat. MOIis the product of mass and the square of a distance which, while not thesame as the balance point, is strongly influenced by the balance point.The closer the balance point is to the handle, the lower the MOI willbe. Several studies have shown that swing speed depends strongly on theMoment of Inertia of the bat—a player can swing a lower inertia batfaster. This affects performance because higher bat speed is directlyrelated to higher batted ball speed. Lowering the inertia of the bat toomuch will result in a lower amount of momentum that the bat carries intothe collision with the ball, reducing the batted ball speed. Ideally, aplayer should use a bat with a high Moment of Inertia and swing it veryfast in order to achieve optimal results. By using a hollow metal batcomprising helical internal ribs, the wall thickness of the bat can bedesigned thinner and the weight savings can be redistributed to thehandle of the bat for an improved CM. Alternatively, the weight can beshifted to the distal tip/cap for increased MOI.

Single-Wall Bats and Multi-Wall Bats

Today, baseball bats and softball bats are frequently made solely fromaluminum alloys, or aluminum alloys in combination with compositematerials (“hybrid bats”), or most recently solely from compositematerials, with the exception being the solid wooden bats used for theMajor Leagues. Such bats are tubular in construction (i.e., hollowinside) in order to meet the weight requirements of the end user, have acylindrical handle portion for gripping, a cylindrical barrel portionfor hitting, and a tapered mid-section for connecting the handle portionto the barrel portion. Traditionally, such hollow metal bats have had aconstant radial stiffness along their barrel portion, measuring theradial stiffness along the barrel wall as independent annular segmentsof the barrel wall at any location along the length of the barrel wall.

When aluminum alloys initially replaced wooden bats in most batcategories, the original aluminum bats were formed as a single member,that is, they were made in a unitary manner as a single-walled aluminumtube for the handle, taper and barrel portions. Such bats are oftencalled single-wall aluminum bats and were known to improve performancerelative to wooden bats as defined by increased hit distance. Morerecently (in the mid 1990's), improvements in bat design largelyconcentrated on further improving bat performance. This was accomplishedprimarily by thinning the barrel wall of the single-wall bat, and addinginner or internal, and/or outer or external, secondary members extendingalong the entire length of the barrel. These members are often referredto, respectively, as inserts or sleeves, while the main member is oftenreferred to as a body, shell or frame. Such bats are often calleddouble-wall bats, or multi-walled bats in the case where two or moresecondary members provide more than two walls. The use of the helicalinternal ribs of the present invention can lighten the inserts and/orsleeves while maintaining bat stiffness/strength.

Such double-walled and multi-walled tubular bats generally obtainimproved performance (in terms of hitting distance) by reason of theimproved elastic deflection that is characteristic of a multi-layerbarrel wall. The efficient batting of a ball is maximized by minimizingplastic deformation, both within the bat and within the ball. Ideally,during the collision between bat and ball, the barrel wall of the batshould not deform beyond its elastic limit. Use of a multi-wall (i.e.,two or more members) construction along the entire barrel length allowsthe barrel portion of the bat to elastically deflect (or flex more) uponball impact, which propels the ball faster and further than single wallbats.

The scientific principle governing improved bat performance is bendingtheory. When a ball impacts a bat, it has kinetic energy that must beabsorbed by the bat in order to stop the ball. The bat stores most ofthis kinetic energy by flexing. The ball deforms as well. After the ballis stopped, the bat returns the energy it has stored by rebounding andsending the ball back towards where it came from. The more the batbarrel deforms upon ball impact without failing (i.e., denting orbreaking) or experiencing plastic deformation, the lower the kineticenergy loss and hence the greater the kinetic energy returned to theball from the bat as the impacted tubular barrel portion of the batreturns to its original shape.

To allow the bat barrel portion to deform requires lowering the radialstiffness of the barrel portion. The prior art double-walled (andmulti-walled) tubular bats have traditionally accomplished this bythinning the main member of the barrel portion and adding thin secondarymember insert(s) and/or sleeve(s) which are not bonded to the mainmember, but which generally extend throughout the full length of thebarrel portion. Such inserts and sleeves are not coupled to the barrelwall portion of the frame, and these two contacting components may slidewith respect to each other in the same manner that leafs slide within aleaf spring. The resultant lowered radial stiffness along the barrelportion length permits the barrel wall to deflect elastically.

U.S. Pat. No. 5,415,398 is an example of a multi-walled bat thatdiscloses the use of a frame and an internal insert of constantthickness running the full length of the barrel portion of the bat in adouble-wall construction.

U.S. Pat. No. 5,303,917 discloses a two-member bat of thermoplastic andcomposite materials.

U.S. Pat. No. 5,364,095 discloses a two-member bat consisting of anexternal metal tube and an internal composite sleeve bonded to theinside of the external metal tube and running the full length of thebarrel portion of the bat.

U.S. Pat. No. 6,251,034 discloses a polymer composite second tubularmember running throughout the full length of the barrel portion of thebat, with the members joined only at the ends of the barrel portion,with the balance of the composite member freely movable relative to theprimary member.

U.S. Pat. Nos. 6,440,017 and 6,612,945 also disclose two-member batswith an outer sleeve and inner shell of constant thickness running thefull length of the barrel portion.

See also U.S. Pat. Nos. 6,063,828, 6,461,760, 6,425,836 and U.S. PatentPublication No. 2001/0094882.

In all of the foregoing prior art multi-walled tubular bats, the batsecondary members (or inserts) extend along the entire frame barrellength, and the bat secondary members have a constant diameter andthickness which results in a uniform cross-sectional geometry along thelength of the secondary members. Also, the bat members are not joined,except at their ends, in order to reduce radial stiffness of the barrelportion and thereby improve bat performance. Also, in all cases, theradial stiffness of the barrel portion is uniform or constant along thefull length of the barrel portion of the bat.

While prior art single member tubular bats and prior art double-walled(and multi-walled) tubular bats have demonstrated improved performance,various regulatory authorities have raised safety concerns regardingimproved performance bats and thus, some have established maximumperformance standards for various categories of bats under theirjurisdiction. As a result, manufacturers of bats are required to passvarious controlled laboratory tests, such as bbf (batted ballperformance), bbs (batted ball speed), etc. Furthermore, for a given batcategory (e.g., “Slowpitch Softball”), there may be two or moreregulatory bodies, each of which may establish a different standard.Furthermore, any of the regulatory bodies may change their standard fromtime to time. Such new or changed or varying regulations are extremelyproblematic, costly, and disruptive for both bat manufacturers andplayers.

It is generally undesirable to lower the performance of a bat by simplyincreasing the thickness of the barrel wall of one or more of the barrelmembers along its full length. This is because lowering the performanceof the bat by merely increasing the wall thickness can increase batweight, which creates new problems with bat weight standards. On theother hand, it can be desirable to increase the wall thickness in thesweetspot, or mid-region, of the barrel portion of the bat withoutsignificantly increasing the weight.

Therefore, what is needed is a simple, low cost approach to vary (e.g.,decrease or at least control) the performance of tubular bats, in orderto meet lowered or changed bat performance standards withoutsignificantly increasing or departing from bat weight standards.Furthermore, in conjunction with causing a decrease in battingperformance, it would be desirable to improve another bat characteristicsuch as “sweetspot” size.

In typical existing single-wall metal bats, material strength andisotropic behavior have limited the degree to which the bat stiffnesscan be altered along the longitudinal axis of the bat. Lowering thestiffness of a bat barrel near the end of the barrel, either at the capor at the tapered section, has generally lowered the durability of thebat due to insufficient material strength. Significantly, the design ofthe present invention (i.e., incorporating helical ribs on the interiorof the metal bat) allows a designer to independently alter the hoop andaxial stiffnesses of a bat barrel along the bat's longitudinal axis.

A multi-wall composite bat with helical internal ribs may offer evenlarger decreases in the barrel stiffness than a single-wall design, andis therefore generally preferred. Again, the helical internal ribs maybe formed on the inner and/or outer sleeves of the multi-wall bat andthe helical ribs may vary in frequency (i.e., number), pitch, height andwidth profile in order to provide the desired performancecharacteristics for the bat. See, for example, FIG. 13A, which shows amulti-wall composite bat having an inner sleeve 15A disposed inside abarrel portion 15, wherein inner sleeve 15A comprises one or morehelical internal ribs 40 (one helical internal rib 40 is shown in FIG.13A). A single-wall barrel, however, can also be enhanced using thehelical internal ribs of the present invention.

Cold-Forming in the Ribs

Flowforming is an advanced, net shape cold metal forming process used tomanufacture precise, tubular components that have largelength-to-diameter ratios. With flowforming, a cylindrical workpiece,sometimes referred to as a “preform”, is fitted over a rotating mandrel.Compression is applied by a set of three hydraulically driven,CNC-controlled rollers to the outside diameter of the preform. Thedesired geometry is achieved when the preform is compressed above itsyield strength and plastically deformed and “made to flow”. As thepreform's wall thickness is reduced by the set of three rollers, thematerial is lengthened and formed over the rotating mandrel. Theflowforming is done cold. Although adiabatic heat is generated from theplastic deformation, the process is flooded with refrigerated coolant todissipate the heat. This ensures that the material is always worked wellbelow its recrystalization temperature. With “cold” flowforming, thematerial's strength and hardness are increased and dimensionalaccuracies are consistently achieved well beyond accuracies that can berealized through hot forming processes.

See FIG. 14, which shows a general setup for a flowforming process.

The present invention preferably uses flowforming to create the helicalinternal ribs of the bat.

Alternatively, the present invention may use flowforming to createlongitudinal ribs on the interior of the bat.

When helical grooves are ground into the flowform mandrel, reciprocatingsplines or ribs can be flowformed into the bore of the flowformed tube,i.e. helical internal ribs can be flowformed onto the inner wall of thebat. In accordance with the present invention, the mandrel grooves canbe longitudinal or helical, although helical grooves are preferred inorder to create the helical internal ribs discussed above. The mandrelgrooves can vary in frequency (i.e., number), pitch, depth and widthprofile along the length of the mandrel, in order to create counterparthelical internal ribs on the bat. FIGS. 15 and 16 are photographsshowing flowformed internal splines, with FIG. 15 showing longitudinalsplines and FIG. 16 showing spiraled splines (i.e., helical internalribs).

In addition to “flowforming in” the splines (i.e., the helical internalribs), there are other cold work processes that can be used to providethe same helical internal ribs in the bore of the barrel, e.g., swaging,impact extruding, drawing over a mandrel (DOM), or a combinationthereof.

Thus, in one form of the present invention, there is provided a novelmetal bat which comprises one or more helical internal ribs which areengineered (e.g., in number, pitch, depth, width profile, etc.) so as toprovide the bat with its desired characteristics. Preferably thesehelical internal ribs are formed by flowforming.

In this respect it should be appreciated that flowforming cansimultaneously vary the wall thickness of the bat and impart the desiredhelical internal ribs to the bat.

Significantly, the present invention provides a novel approach to shiftand modify wall thickness/weight/modulus and geometry along the lengthof the bat.

As noted above, the present invention uses helical internal ribs totune/control the stiffness of the barrel of the bat so as to maximizethe trampoline effect for peak bat performance, yet still keep the batcompliant with BBCOR regulations and/or other regulations. The provisionof helical internal ribs can strategically take weight out of the barrelin certain areas to allow for a redistribution of the weight in otherareas, if desired. By way of example but not limitation, putting weightat the handle allows the bat to be swung faster, putting weight at thedistal (cap) end helps with bat Moment of Inertia, etc.

Being able to make lighter barrels and shells (double wall bats)utilizing helical internal ribs is also advantageous because the ribbedbarrel/shell composite may equal the weight of a heavier single-walledbat but with enhanced/tuned, engineered stiffness/trampoline effect.

Furthermore, it should be appreciated that when a bat bends duringcontact with a ball, the bat does not snap back perfectly uniformly.Rather, the bat will tend to collapse in hoop, bend and twist back intorsion, in a “shear” bending mode. If the spiral ribs are formedclockwise it could help to counteract the shear bending mode forrighthand batters. If the spiral ribs are formed counter-clockwise, itwould help the shear bending mode for lefthand batters. Thus, theintentional directionality of the helical ribs can be used to helpcounteract the forces of the bat's natural shear bending mode, and tohelp the “trampoline effect” of the bat to pop balls upward rather thandriving balls into the ground. Alternatively, in some situations, it maybe desirable to cause the bat to drive the ball into the ground. Abarrel with a biased, torsional twist would be advantageous in hittingthe ball into the ground. Thus, in this form of the invention, a “lefthanded” bat or a “right handed” bat may be produced.

The spiral internal ribs may be provided in the handle and taper sectionof the bat in addition to the barrel section of the bat, because thecounter-opposing spiral ribbing could have benefits in the taperedtransition bending area too.

And in another form of the invention, there is provided a novel hollowmetal bat which comprises longitudinal inner ribs which are formed byflowforming. Flowforming the longitudinal ribs, rather than forming themby casting as with the prior art, is a significant advantage over theprior art.

EXAMPLE

By way of example but not limitation, in one preferred form of theinvention, hollow metal bat 5 may be formed out of aluminum, may have abarrel wall thickness of 0.092″, and may have a single helical internalrib 40 having a pitch of one revolution over 12″ and a rib height of0.050″ (off the floor of the barrel wall).

MODIFICATIONS

It will be understood that many changes in the details, materials, stepsand arrangements of elements, which have been herein described andillustrated in order to explain the nature of the invention, may be madeby those skilled in the art without departing from the scope of thepresent invention.

1. A hollow metal bat comprising an elongated tubular structure having abarrel portion, a handle portion and a tapered portion connecting thebarrel portion to the handle portion, and further comprising at leastone helical internal rib formed along at least a portion of theelongated tubular structure.
 2. A hollow metal bat according to claim 1wherein the at least one helical internal rib is formed along at least aportion of the barrel portion.
 3. A hollow metal bat according to claim1 wherein the at least one helical internal rib is formed along theentire barrel portion.
 4. A hollow metal bat according to claim 1wherein the at least one helical internal rib is formed along the entireelongated tubular structure.
 5. A hollow metal bat according to claim 1wherein the at least one helical internal rib has a clockwiseorientation as the helical internal rib extends distally down the bat.6. A hollow metal bat according to claim 1 wherein the at least onehelical internal rib has a counter-clockwise orientation as the helicalinternal rib extends distally down the bat.
 7. A hollow metal bataccording to claim 1 wherein the bat is formed by flowforming.
 8. Ahollow metal bat according to claim 1 wherein the bat is formed by atleast one from the group consisting of swaging, impact extruding,drawing over a mandrel (DOM), machining, and casting.
 9. A hollow metalbat according to claim 1 wherein the at least one helical internal ribhas its pitch, height and width profile tailored to provide the desiredcharacteristics for the bat.
 10. A hollow metal bat according to claim 9wherein the pitch, height and width of the at least one helical internalrib is selected so that the bat has a BBCOR of 0.500 or less.
 11. Ahollow metal bat according to claim 1 wherein the bat comprises aplurality of helical internal ribs.
 12. A hollow metal bat according toclaim 11 wherein the plurality of helical internal ribs have theirnumber, pitch, height and width profile tailored so as to provide thedesired characteristics for the bat.
 13. A hollow metal bat according toclaim 12 wherein the number, pitch, height and width of the plurality ofhelical internal ribs is selected so that the bat has a BBCOR of 0.500or less.
 14. A hollow metal bat according to claim 1 wherein the batcomprises a multi-wall construction.
 15. A hollow metal bat according toclaim 14 wherein the multi-wall construction comprises a sleeve disposedcoaxial with the barrel portion, and further wherein the at least onehelical internal rib is formed on the interior of the sleeve.
 16. Ahollow metal bat according to claim 14 wherein the multi-wallconstruction comprises a sleeve disposed coaxial with the barrelportion, and further wherein the at least one helical internal rib isformed on the exterior of the sleeve.
 17. A method for forming a hollowmetal bat, the method comprising: positioning a preform on a mandrel,wherein the mandrel comprises at least one helical groove; and applyingcompression to the outside diameter of the preform so as to form anelongated tubular structure having a barrel portion, a handle portionand a tapered portion connecting the barrel portion to the handleportion, and further comprising at least one helical internal rib formedalong at least a portion of the elongated tubular structure.